1. Field of the Invention
The present invention relates to a liquid discharging method comprising discharging a desired liquid in a desired state by using bubbles generated by applying thermal energy to the liquid, and a liquid discharging head for use in the liquid discharging method. The present invention can be preferably applied to a field of ink-jet recording technology.
The invention can be applied to equipment such as printers, copying machines, facsimiles having a communication system and word processors having a printing part, as well as industrial recording apparatuses combined with various processors, which can record on recording media such as paper, thread, fiber, cloth, leather, metals, plastics, glass, wood and ceramics.
The term "recording" as used in the present invention means not only the application of images with meaning such as letters and designs to the recording media, but also the application of such images having no meaning as patterns thereto.
2. Related Background Art
It has been known an ink-discharge recording method, so-called bubble-discharge recording method, in which the application of energy such as heat to ink causes a change of state accompanied by the rapid volumetric change (generation of bubbles) in the ink, and the ink is discharged out from the discharge opening by the working force generated from this state change, and applied to a recording medium, thereby forming an image. As disclosed in U.S. Pat. No. 4,723,129, the recording apparatus utilizing this bubble-discharge recording method is generally equipped with discharge openings for ink discharge, an ink flow path communicating with the discharge openings, and an electrothermal converting element as an energy-generating means for discharging the ink in the ink flow path.
This recording method has many merits, that is, in addition to printing of high-quality image at a high speed with slight noise, a small-sized apparatus can provides high-resolution of recorded images as well as color images, since the discharge openings for ink discharge can be arranged at a high density in a printing head. Therefore, recently the bubble-discharge recording method has been used in many office machines such as printers, copying machines and facsimiles and also in industrial systems such as textile printing apparatus.
As the bubble-discharge technology has been used in products of various fields as described above, the following various demands have been increasing in recent years.
For example, as to the demand for improvement in energy efficiency, there has been proposed the optimization of the heating element such as the thickness control of the protective film. This technique is effective in improving the propagation efficiency of the generated heat to the liquid.
In order to obtain high-quality images, there are proposed drive conditions for the liquid-discharge process with a high ink discharge speed as well as good ink discharge based on the stable bubble generation and the like. For the high speed recording, there is proposed an improved flow path form to provide a liquid-discharge head which can refill the liquid flow path with the liquid in a high speed after the liquid discharge.
For the flow path forms, flow path structures illustrated in FIGS. 23A and 23B are disclosed in Japanese Patent Application Laid-Open No. 63-199972 etc. The flow path structure and production process of the head described in this publication were invented by paying attention to the back wave (pressure toward the direction opposite to the discharge opening, i.e., pressure toward a liquid chamber 12) generated with the generation of bubbles. This back wave is an energy loss because it is not energy toward the discharging direction.
The invention illustrated in FIGS. 23A and 23B discloses valve 10, separated from a bubble-generating region which is defined by heating element 2, and situated opposite to discharge opening 11 in relation to the heating element 2.
In FIG. 23B, it is disclosed that the valve 10 produced by a production method making use of a plate sticks on the top of flow path 3 in the initial position, and hangs down within the flow path 3 with the generation of bubbles. The invention discloses that the loss of energy is prevented by controlling a part of the above-described back wave by the valve 10.
In this structure, however, the control of a part of the back wave by the valve 10 is not practical for the liquid discharge, apparent from studying the generation of bubbles within the flow path 3 holding the liquid to be discharged. The reason is as follows.
As described above, the back wave itself is not directly related to the discharge. At the time the back wave occurs within the flow path 3, the pressure from the bubble involved in the discharge has already made the liquid ejectable from the flow path 3 as illustrated in FIG. 23B. Accordingly, it is apparent that the control of a part of the back wave does not exert a great influence on the discharge.
On the other hand, in the bubble-discharge recording method, deposit is formed on the surface of the heating element due to the scorching ink since heating is repeated in the presence of the ink. Depending on the ink used, the deposit is formed in a large amount, and so the generation of bubbles becomes unstable. Therefore, sometimes there have been difficulties in successfully discharging the ink. Besides, there has been a demand for a good discharge method without the deterioration of the liquid to be discharged even when the liquid is heat-liable or has difficulty in sufficient bubble formation.
From such a point of view, a process in which the liquid which generates bubbles by heating (bubbling liquid) and the liquid to be discharged (discharge liquid) are different, and the discharge liquid is discharged by the transmitted pressure generated by bubbling of the bubbling liquid has been disclosed in, for example, Japanese Patent Application Laid-Open Nos. 61-69467 and 55-81172, and U.S. Pat. No. 4,480,259. According to these publications, an ink as the discharge liquid and the bubbling liquid are completely separated from each other by a flexible membrane such as silicone rubber to prevent the discharge liquid from direct contact with the heating element, and the pressure generated by the bubbling of the bubbling liquid is transmitted to the discharge liquid by deformation of the flexible membrane. Such a construction permits the prevention of deposit formation on the surface of the heating element and the improves the freedom of the selection of the discharge liquid.
However, in a head where the discharge liquid is completely separated from the bubbling liquid as described above, a considerable amount of the pressure generated by bubbling is absorbed in the flexible membrane because the pressure upon bubbling is transmitted to the discharge liquid by the deformation of the flexible membrane by expansion or shrinkage. Besides, since the amount of deformation of the flexible membrane is not very great, there has been a possibility that energy efficiency and discharging force may be lowered although the separation of the discharge liquid from the bubbling liquid is effective.